This invention relates to optical diagnosis and correction, and in particular provides methods, devices, and systems for treating presbyopia and other vision conditions, for evaluating and deriving prescriptions for treatment of presbyopia and other vision conditions, and/or for measuring the response of the eye to different viewing conditions.
Presbyopia is a condition that affects the accommodation properties of the eye. As objects move closer to a young, properly functioning eye, ciliary muscle contraction and zonular relaxation allow the lens of the eye to become rounder or more convex, and thus increase its optical power and ability to focus at near distances. Accommodation can allow the eye to focus and refocus between near and far objects.
Presbyopia normally develops as a person ages, and is associated with a natural progressive loss of accommodation, sometimes referred to as “old sight.” The presbyopic eye often loses the ability to rapidly and easily refocus on objects at varying distances. There may also be a loss in the ability to focus on objects at near distances. Although the condition progresses over the lifetime of an individual, the effects of presbyopia usually become noticeable after the age of 45 years. By the age of 65 years, the crystalline lens has often lost almost all elastic properties and has only limited ability to change shape. Residual accommodation refers to the amount of accommodation that remains in the eye. A lower degree of residual accommodation contributes to more severe presbyopia, whereas a higher amount of residual accommodation correlates with less severe presbyopia.
Known methods and devices for treating presbyopia seek to provide vision approaching that of an emmetropic eye. In an emmetropic eye, both distant objects and near objects can be seen due to the accommodation properties of the eye. To address the vision problems associated with presbyopia, reading glasses have traditionally been used by individuals to add plus power diopter to the eye, thus allowing the eye to focus on near objects and maintain a clear image. This approach is similar to that of treating hyperopia, or farsightedness.
Presbyopia has also been treated with bi-focal eyeglasses, where one portion of the lens is corrected for distance vision, and another portion of the lens is corrected for near vision. When peering down through the bifocals, the individual looks through the portion of the lens corrected for near vision. When viewing distant objects, the individual looks higher, through the portion of the bi-focals corrected for distance vision. Thus with little or no accommodation, the individual can see both far and near objects.
Contact lenses and intra-ocular lenses (IOLs) have also been used to treat presbyopia. One approach is to provide the individual with monovision, where one eye (usually the primary eye) is corrected for distance-vision, while the other eye is corrected for near-vision. Unfortunately, with monovision the individual may not clearly see objects that are intermediately positioned because the object is out-of-focus for both eyes. Also, an individual may have trouble seeing with only one eye, or may be unable to tolerate an imbalance between their eyes. In addition to monovision, other approaches include bilateral correction with either bi-focal or multi-focal lenses. In the case of bi-focal lenses, the lens is made so that both a distant point and a near point can be focused. In the multi-focal case, there may exist many focal points between near targets and far targets.
In the field of refractive surgery, certain ablation profiles have been suggested to treat the condition, often with the goal of increasing the range of focus of the eye (rather than restoring accommodation in the patient's eye). Many of these ablation profiles can provide a single excellent focus of the eye, yet they do not provide an increased depth of focus such that optimal distance acuity, optimal near acuity, and acceptable intermediate acuity occur simultaneously. Shapes have been proposed for providing enhanced distance and near vision, yet current approaches do not provide ideal results for all patients.
Prior presbyopia treatment may generally be categorized into two approaches: passive and active. Active treatments generally seek to restore accommodation, such as through the use of an artificial accommodating intra-ocular lenses (IOLs), scleral expansion bands (SEBs), and drug therapies. Passive treatments generally seek to change the optical properties of the human eye to maintain an acceptable compromise between near vision and distance vision. Passive treatments include multifocal and bifocal contact lenses, IOLs, spectacle lenses, monovision, and the like. Effectiveness of both active and passive techniques has generally been established by human clinical trials which are time-consuming, expensive and may involve some risk for the involved patients. Optical modeling can provide significant insight into proposed techniques, but substantial uncertainties remain, including those associated with the retinal response and neural processing of the optical signals transmitted through the ocular optics.
In light of the above, it would be desirable to have improved methods, devices, and systems for treatment of presbyopia and other vision defects. It would also be desirable to have improved methods, devices, and systems for measuring the optical and/or visual response of the human viewing system and for developing new prescriptions to treat presbyopia and other viewing defects. It would generally be desirable to increase the percentage of the population which can be effectively treated for presbyopia and other vision defects without greatly increasing the cost, risk, and/or complexity of diagnosis and/or treatment over current techniques.